Compression mold



Feb. 6, 1945.

c. F. MARscHNER 2,368,717

COMPRES S ION MOLD Filed May 17, 1943 4 /^//f^/me. Mig-MM,

Ww 4 H M Patented Feb. 6, 1945 'UNITED' lSTATES PATENT OFFICE COMPRESSION MOLD Charles F. Marschner, Normandy, Mo., assis-nor to McDonnell Aircraft Corporation, St. Louis, Mo., a corporation of Maryland Application May 17, 1943, Serial No. 487,297

(Cl. 18-4l 2) 1 Claim.

die member which will cooperate with the heated cavity or female die member of the compression Y mold to form a molded plastic part that is free from'wrinkles and buckles and that may have accurately formed flanges, ribs and sharp radii thereon and openings therein. -The invention consists in providing the plunger or male die member of the compression .mold wtih a rigid hard-surfaced bottom section,` preferably of molded plastic, a rigid top section, preferably of asbestos,l and a resilient intermediate section, preferably of vrubber bondedto said top and bottom plates.v The invention also consists in the parts and in the arrangements and combinations of parts hereinafter described and claimed.' Y In the `accompanying drawing, which forms part vof this specification and wherein like symb'ols refer to likeparts wherever they occur,

Fig. 1 is a vertical sectional view of an open '.compression mold provided withv a composite plunger or male die member embodying my invention,V

Fig. 2 is a vertical sectional View of the closed compression mold, showing the distribution of the molding pressure,

Fig. 3 is abottom perspective View of a portion of the male die member; and

Fig. 4 is a perspective View of the plastic part formed in said compression mold.

The present compression mold comprises a heated female die member A, which is preferably made of metal and has a suitably shaped mold cavity or recess I in the top thereof, and a composite plunger or male die memberB adapted to be engaged with or secured to a die press ram (not shown) for vertical movement into and out of said mold cavity or recess. As shown in the drawing, the mold cavity I and the male die member B may be shaped to form therebetween a plastic part C comprising -a web 2 with one or p more strengthening beads- 3 and/or bosses 4 and side flanges 5 connectedto said web by comparativelysharp bends or radii 6. .The composite plunger or `male die member B of the compressionmold comprises a rigid bottom section 1, a rigid topsection 8- and a resilient intermediate section 9 interposed between and bonded to said top and bottom sections. The rigid bottom section 'I of the male die meml ates with the side walls ofthe mold cavity I -to v ber B is preferably made in the form of a hardsurfaced plate of molded plastic adapted tocooperate with the similarly shaped lower portion -of` the mold cavity I- of the female die member A to formA the web 2, bead 3, bossesA 4 and radii 6 of the molded plastic :part C.

The rigid top or section 8 of the male die memberAB comprises, a plateofv plastic, metal,

wood or other `rigid material which fits within the top of the mold cavity and forms the marginal edges of the side flanges-5 of the molded part C. When made of metal the sides of the top plates function as shear edges for pinch-.trimming theV flash at said marginal edges of said side anges. vThe top or backingv plate, however, is

preferably made of asbestos,l which provides sufcient rigidity ,and an even distribution of the pressure and also serves as a heat insulator.l

The resilient intermediate section `of. the plunger or male die member B of the compression mold is preferably made of rubber which is vulcanized to theplastic bottom plate 'I andto the asbestos top or backingplate and cooperform the side iianges 5 of the molded part C. This resilient member may, however, be rmade of synthetic rubber, plastic material, fibrous material .impregnated with rubber,` or any other material which is deformable and is capable of recovering its size and shape after deformation.

In operation, the molding compound is placed vin the mold cavity I of the heated female die member A and the plunger or male die member B is forced downwardly into said mold cavity to form the plastic article or part C. The asbestos backing plate provides an even distribution of' the molding pressure over the entire area of the resilient intermediate section 9 of the male die member B, while said resilient intermediate section evenly distributes such pressure over the entire area of the plastic bottom plate 1 of said male die member. The hard-surfaced bottom plate 1 prevents wrinkling or buckling of the web portion 2 of the molded plastic part C and accurately forms the .bead 3 and bossesv 4 therein and also the sharp bends or radii 6 that connectl the side flanges 5 to said web. The vertical compression applied to the .resilient vintermediate section 9 of the male die member `B causes said section to expand or ow laterally in a fluidlike manner towards the sides of the mold cavity I, thus' supplying the side. pressure required to accurately form the vertical sideflanges 5 of the molded part C. This lateral expansion of the resilient intermediate member .9 -under the molding pressure also permits the formation of molded C from said die after molding.

The plastic bottom plate l is preferably molded directlyin the mold cavity I of the female die member A. While thismanner of molding the bottonil plate I does not initially provide the proper clearance spacel between said plate and the mold cavity I, such clearance is obtained by incomplete curing of the bottom plate in the mold cavity and then completely curing the semi cured plastic in said cavity by molding several plastic'parts in the mold. During these rst few molding operations the partly` cured bottom plate will ow to the proper shape,v and the heat from said molding operations will bring abouta complete polymerization of the plastic and thus cause the plate to set or completely cure in the desired shape.

Obviously, the hereinbefore described compression mold'admlts of considerable modification without departing from the invention. There- `fore, I do not wish to be limited to the precise arrangement shown'and described.

What I claim is:l

A mold for pressure molding a plastic article having a web with side flanges connected thereto by comparatively sharp radii, said mold comprising a metal female die member having a mold cavity thereinanda male die member cooperating withsaid ycavity for pressure molding said plastic 'v article therein, said male die comprising a suhstantially rigid top section, a rigid hard-surfaced bottom section of molded plastic and a rubber ,intermediate section interposed between and vulcanized to said top and bottom sections, said rigid hard-surfaced molded plastic bottom section constituting the entire lower portion of said male die, whereby said intermediate rubber section cooperates with said die cavity to form the side flanges only of said plastic larticle and said rigid hardsurfaced molded plastic bottom section cooperates with said cavity to form the web of said plastic article and the relatively sharp radii thereof that connect said side anges to said web.

CHARLES F. MARSCHNER. 

